1. Field of the Invention
The invention relates to a motor vehicle lid or door lock, especially to a tailgate lock. In particular, the invention is directed to such a lock which has a front catch, a main catch, and a lock latch which can be moved from and open position into a front catch position and into a main catch position and vice versa, with a detent pawl which keeps the lock latch in the front catch position and main catch position and a corresponding catch projection and actuating surface, as well as with a motorized, preferably electric motor drive with drive element having a driver located thereon. Still further, to such a lock in which, by turning the drive element in one direction, i.e., a lifting and rotating direction, the driver strikes the actuating surface and lifts the catch projection of the detent pawl out of the main catch, and in which the drive is turned off after the lifting process with the detent pawl remaining in the lifted position
2. Description of Related Art
The known motor vehicle deck lock or door lock on which the invention is based (German Patent Application A-32 42 527) is described in the prior art as a motor vehicle side door lock. This lock has an extensive motorized drive, specifically an electric motor. Both the lock latch and the detent pawl are driven by an electric motor, the lock latch being a closing aid, and the detent pawl being an electric motor trigger. Prior art shows specifically only a single electric drive motor which can be coupled by drive engineering both to the lock latch (in one direction of rotation) and also to the detent pawl (in the other direction of rotation) via a step-down gear which works in two directions. Only the electric motor drive in its relation to the detent pawl is of interest for the teaching of the present invention.
In the aforementioned prior art, the lock latch is provided with a double detent which is conventional for side door locks, specifically as a fork latch made with a front catch on the forward fork latch leg and a main catch on the after fork latch leg. The lock latch is held in the front catch position and in the main catch position by a tension-loaded detent pawl with a corresponding catch projection. The detent pawl is supported on a bearing axis and has two arms, the second arm of the detent pawl pointing away from the catch projection having an actuating surface. The electric motor drive has a drive element made as a pinion, to which a driver in the form of a cam disk is attached, with a stop edge which forms an eccentric driver. This drive element can only rotate in one direction, and therefore, is not set back, but always continues to return to its initial position in the direction of rotation. By turning the drive element in the lifting and rotating direction, the driver strikes the actuating surface of the detent pawl and lifts the catch projection of the detent pawl out of the main catch on the rotary latch.
In the prior art explained above, starting of the electric motor drive is triggered by actuating a handle, for example, an outside door handle; this actuation switches a microswitch. After successfully lifting the detent pawl out of the main catch by means of the driver, the driver stops on another microswitch and first shuts off the electric motor drive again. In doing so, the detent pawl remains in the lifted position. In this way, the rotary latch can reach its opening position unhindered by the detent pawl, and therefore, the detent pawl does not descend into the front catch of the rotary latch. This state lasts until the handle, for example, the outside door handle, is released. Releasing the handle switches the first switch again, which thus turns on the electric motor drive again. The cam disk which forms the driver continues to turn into its initial position in which the detent pawl drops back again or rests on the front fork latch leg under force of the reset spring. When the vehicle door or tailgate is closed the detent pawl can, therefore, drop again into the front catch on the lock latch under the spring force.
The aforementioned explanation illustrates that the proper function of holding the detent pawl open presupposes positive actuation of the handle by a person. When a person releases the handle before the rotary latch has reached the open position, it can happen that the detent pawl drops into the front catch of the rotary latch although the door or lid has not yet completely opened. This is not very problematical in this type of drive engineering since further pulling on the handle allows the trigger cycle for the detent pawl to be repeated. The entire control system, however, assumes the use of different microswitches; this is problematical with regard to operating reliability.
Motor vehicle locks are known in which the opening motion can be triggered solely by a switching measure, in which, therefore, positive actuation of a handle, such as the outside door handle, and holding of the handle are not a prerequisite for the above explained operation. In these locks there is a so-called "snow load lever" (German Patent C-38 01 581). A "snow load lever" is an additional lever which, when the lifting position of the detent pawl is reached, drops relative to the detent pawl such that the detent pawl is held in the lifted position until the rotary latch has reached its open position. In this position the "snow load lever" is swivelled free of the detent pawl so that it is again operable with respect to the front catch of the rotary latch. This mechanical technique is a proven and feasible one, since it solves the problem of a lid or door which does not open by itself, for example, when loaded by snow, when the reset force of the seal is not sufficient, or when the seal is frozen solid (otherwise, either two persons would have to switch on the one hand and open on the other, or the electric motor drive would run continually back and forth). The mechanical solution with the additional "snow load lever" is, however, a problem in terms of cost from the current standpoint; any additional lever with a bearing spike and pretensioning spring in a motor vehicle lock represents a cost factor, but also a risk factor (sticking, breaking). The solution known from practice with the mechanical "snow load lever" is therefore not optimum either.
In a motor vehicle lock in which lifting of the detent pawl is caused by purely electrical means, especially via a solenoid, a "snow load function" can be accomplished by purely control engineering means, if the corresponding switching functions are provided. Then, the rotary motion of the rotary latch must be scanned until the open position is reached. This in turn requires microswitches.
Furthermore, a motor vehicle lock is known in which the lock latch has only one main catch, and therefore, there is no front catch (German Patent C-39 32 268). Here, there is an electric motor drive which is not self-locking, but is reset into its initial position by means of spring force when the power supply current is turned off. In this motor vehicle lid lock, there is an elastic stop for the detent pawl and its lifted position. As soon as the detent pawl has reached the elastic stop, and thus its lifted position, the electric motor drive is turned off. The drive element which is made as a disk and which represents the worm wheel of an electric motor worm drive is turned backwards around its axis of rotation by a pretensioned reset spring, and in this way, is returned to its initial position. The driver thus returns by the reverse running direction into its initial position on the same path on which it has approached the actuating surface of the detent pawl on the way there. Here it is provided that the lock latch which is in the open position keeps the detent pawl in the lifted position. When the lid is then closed, the lock latch easily releases the detent pawl and the pawl can return to the drop position under the action of a spring. This concept cannot easily be applied to motor vehicle locks with a front catch and a main catch.